Seat backs, particularly those of motor vehicles, are often equipped with power- or manually-operated mechanisms for adjusting the back's lumbar contour to suit passenger preference. Such adjustable lumbar supports have achieved popularity despite their complexity and relatively high cost, their tendency to jam or break in operation, and the difficulty and expense of their repair or replacement.
Another common shortcoming of current lumbar support assemblies is that while they may be capable of manual- or power-operated adjustment, they often lack the limited self-adjustability required for user comfort should, for example, an occupant shift in position and exert greater force against one side or the other of the seat back. Also, while increased lumbar support may be desirable for passenger/driver comfort over an extended interval, it may be undesirable in certain situations as, for example, when the localized force against an occupant's back is suddenly increased by reason of a severe rear end collision.
References indicative of the state of the art are U.S. Pat. Nos. 4,354,709, 4,295,681, 3,724,144, 5,088,790, 4,880,271, 4,452,485, 5,013,087, 5,011,223, 3,890,000, 4,465,317, 4,469,374, 4,556,251, and 4,576,410.
Important aspects of this invention lie in providing an adjustable lumbar support assembly that is relatively simple and inexpensive in construction, operates smoothly and reliably without risk of jamming, especially at the limits of its range of operation, is capable of limited self-adjustment when seated occupant shifts laterally, and is potentially self-releasing should forces in the lumbar region suddenly become excessive, as in the case of a severe rear-end impact against the occupant's vehicle.
Briefly, the assembly includes a mounting bracket adapted for connection to a seat back frame or, in the case of an integrated structure, a frame equipped with such a bracket. The bracket includes a pair of laterally-spaced side portions that define aligned, horizontally-spaced channels. A pair of glide blocks are mounted for horizontal sliding movement along the channels, and a curved, tensioned, horizontally-elongated leaf spring has its opposite ends operatively connected to the glide blocks with its mid-portion bowed away from the bracket. The bracket includes means for rotatably supporting a threaded shaft and means for operatively connecting the glide blocks and threaded shaft (e.g., a nut carried by the shaft and cables connecting the nut and glide blocks) for movement of the blocks towards and away from each other as the shaft is rotated in one direction or the other. A contoured back support plate is connected to the intermediate portion of the leaf spring, and control means, either manual or power-operated, is provided for selectively rotating the shaft for shifting the glide blocks to adjust the extent of curvature of the leaf spring.
The contoured back support plate is connected to the spring only along the mid-portion of the plate to allow limited movement of the plate's side portions towards and away from the spring in response to unequal loading against those side portions, thereby providing limited self-adjustment of the lumbar support assembly. Each of the glide blocks is provided with an undercut shoulder for receiving an end portion of the leaf spring and, should severe forces be generated that substantially reverse the curvature of the spring, as in the case of a rear-end impact, the ends of the spring are mounted to release from the undercut shoulders.
In a preferred embodiment, the threaded shaft of the adjustment mechanism is supported by the mounting bracket for rotation about a generally vertical axis, and the means for connecting the glide blocks and threaded shaft includes a nut carried by the shaft for movement between raised and lowered positions. Connecting means such as cables operatively connect the nut to each of the glide blocks for shifting the blocks towards and away from each other to alter the curvature of the spring as the shaft is rotated in one direction or the other.
Jamming at the extreme upper and lower positions of the nut is prevented by providing the threaded shaft with radially-extending abutment means at its upper and lower ends. The nut is also provided with radially-extending stop means, with such stop means being disposed directly in the path of rotational movement of the abutment means, to prevent, by direct and positive blocking or abutting action, continued rotation of the shaft in the same (non-reversing) direction when the nut reaches the upper or lower limits of its travel.
Other features, advantages, and objects of the invention will become apparent from the specification and drawings.